Process for supplying heat to a bed of finely divided refractory material



' United Stat Pate-m CHIC? PROCESS FOR SUPPIJYING HEAT TO A BED OFFINELY DIVIDED REFRACTORY Geert G. Kruijer, The Hague, Netherlands,assignor to Shell Oil Company, a corporation of Delaware No Drawing.Filed Nov. 18, 19 57, Ser. No. 696,968 Claims priority, applicationNetherlands Nov. 20, 1956 '6 Claims. (Cl. 26352) This invention relatesto the transmission of heat by means of finely divided refractorymaterial and is more particularly concerned with a process wherein a gasstream is used to maintain the material in a fluidized state, namely, ina flowing state of a dense turbulent suspension and to heat the materialat the same time.

It is known to heat particles of a bed of finely divided material whichare fluidized by means of a gas stream by injecting therein and burninga fuel in direct contact therewith. During the combustion of the fuelthe particles of the finely divided material should be retained in thefluidized state into which'they were brought by the gas steam.

It has been found that the temperature at which the fuel is burnt in thefluidized bed of finely divided refractory material should be keptrelatively low on account of the presence of solids which melt or fluxat a relatively low temperature during the combustion of the fuel.

A method to overcome this difliculty has been suggested in which thecombustion of the fuel and the fluidization of the finely dividedmaterial is effected in separate spaces separated from each other by awall with which both the fuel and the finely divided material come intocontact (see British patent specification 665,723).

Methods are also known for the preparation of a gas mixturesubstantially comprising carbon monoxide and hydrogen by partiallyburning liquid bituminous material such as heavy tars, heavydistillation residues of mineral oils or natural asphalts, in a bed of afinely divided refractory material, such as silica, which is maintainedin the fluidized state of a dense turbulent suspension by an upward gasstream of a mixture of oxygen and steam. If the bitumen contains saltsor other compounds of metals such as vanadium, which is usually thecase, the powdered, refractory material is contaminated thereby. As thesalts or metallic compounds occurring in the starting material generallydo not melt at the relatively low temperature at which the partialcombustion of the bituminous material is carried out, fresh powderedrefractory material may be supplied continuously (see US. patentspecification 2,605,178).

Tests have shown that in a fluidized bed of finely divided material suchas sand, the particles thereof sinter when a fuel containing sodium,vanadium or both metals is burnt in this bed at a temperature in excessof that at which the ash formed during combustion melts or fluxes.Sintering phenomena do not occur in a sand bed at a temperature of 900C. when the sodium content is lower than 0.03% calculated as sodiumoxide. Under the same conditions, they do not occur either when thevanadium content in the sand bed is lower than 0.1%, calculated asvanadium pentoxide. The temperature above which sintering phenomena mayoccur in a sand bed is approximately 600 C.900 C. Apparently a layer ofmolten ash is formed round the particles of the finely dividedrefractory material, as a result of which there is an interference ofthe fiuidization. Lumps types of suitable compounds are 2 may even beformed which entirely prevent fluidization of the bed.

It has been found that the addition of an admixture containing certainmetals prevents sinteringphenomena in the bed, egg. of sand, even iffuels containing sodium and/or vanadium are burnt in the fluidizedbed ata temperature higher than the melting or fluxing temperature of the ashformed during the combustion of these fuels in the absence of theadmixture, and even if the bed contains a relatively high content ofsodium, vanadium or both.

Accordingly, the invention relates to a process for the supply of heatto a bed finely divided refractory material maintained in a fluidizedstate by a gas stream by the combustion of a liquid fuel in directcontact with the finely divided refractory material.

According to the invention a liquid fuel containing sodium and/orvanadium is burnt in the bed of finely divided material in the presenceof an admixture containing one or more metals of groups II and III ofthe periodic table.

This admixture may tinuously and discontinuously, either directly orindirectly. A simple method of supply is to spray the admixture in 'afinely divided form into the bed together with a gas, for instance theair with which the bed is fluidized and the fuel is burnt. However, itis also possible to dissolve or to suspend the admixture in a liquid andto spray the latter into the bed or add it thereto: in another way. Ifthe admixture has to be suspended in the liquid, a dispersant or asurface-active substance may also be added thereto. The liquid may be agas oil or other petroleum hydrocarbon fuel.

The admixture may be a simple substance or a mixture of compounds eachof which may contain one or more metals of groups 11 and III. Theadmixture may be wholly or partly inorganic or organic and may thereforeconsist of an inorganic or organic compound, or a mixture of inorganicor organic compounds. The most effective compounds are magnesiumcompounds such as magnesium oxide or magnesium naphthenate. Otheraluminum compounds such as alumina, zinc compounds such as zinc oxide,and calcium compounds such as calcium oxide. The compounds may beeither. of synthetic o-r natural origin. Thus dolomite or talc may alsobe used for the purpose of the invention.

The process according to the invention is illustrated by" the followingexamples. All percentages are percentages by weight unless expresslystated otherwise.

Example I Sand already containing ash formed by the combustion of aliquid fuel containing sodium and having a sodium content of 0.1%,calculated as sodium oxide, was heated without an admixture for 5 hoursat 900 C. The sand sintered. When the sand also contained 0.5% magnesiumoxide (MgO), alumina (A1 0 or zinc oxide (ZnO) sinter-ing was prevented.

Example 11 Example 111 Results similar to those given in Examples I andII were obtained with sand already containing ash formed .Patented July12, 1960,

be added to the bed both conoccurred in the sand, but when at least 0.5%magnesium oxide, at least 3% alumina or at least 5% zinc oxide wereadded to the sand no sintering phenomena were observed.

Example IV A substance containing sodium was added to a liquid fuel, sothat the percentage of sodium in the fuel was 0.4%, calculated as sodiumoxide. This fuel containing sodium was burnt in a fluidized sand bed ata temperature of 900 to 950 C. The quantity of liquid supplied daily was500 kg, while the quantity of admixture consisting of magnesium oxidesupplied daily to the sand bed was gradually reduced from 7 /2 kg. to 2.kg. per diem. Towards the end of the test, which lasted for 760 hours,the sand contained 4.55% Mg, calculated as MgO, to slightly more than 3%sodium, calculated as sodium oxide, viz. in the approximate ratio of1.5:1. Difiiculties on account of sintering in the sand bed were notexperienced.

Example V A fuel oil with a specific gravity of 0.96, an ash content of0.096% and a V content of the ash of 67% was burnt in a fluidized sandbed at a temperature of 900950 C. The quantity of fuel supplied daily tothe sand was 500 kg., while the quantity of admixture consisting ofmagnesium oxide supplied to the sand bed was gradually reduced from 8kg. per diem to 2 kg. per diem. Difliculties on account of sintering inthe sand bed were not experienced in this test either which lastedlonger than 2,000 hours.

Example VI A fuel oil with a specific gravity of 0.96, an ash content of0.2%, a V 0 content of the ash of 42% and an Na C content of 42% wasburnt in a fluidized sand bed at a temperature of 900 C. The quantity offuel supplied daily to the sand was 500 kg., while the quantity ofadmixture consisting of magnesium oxide supplied to the sand bed wasgradually reduced from 8 kg. per diem to 2 kg. per diem. The test lasted2,000 hours. There were no difiiculties on account of sintering in thesand bed.

Example VII This experiment was carried out with a sand sample whichalready contained ash formed by the combustion of a liquid fuelcontaining sodium. This sample, having a sodium content of 3.0%,calculated as sodium When. heated for 5 hours at a temperature of 900 C.sinterin-g oxide, was heated without an additive for 5 hours at 900 C.The sand sintered. When the sand sample also contained 1%, 5%, 10% or20% by weight of calcium oxide (CaO), sintering was prevented. Thedegree of sintering decreased as the sand sample contained more calciumoxide. 1

Example VII This experiment was carried out with a sand sample whichalready contained ash formed by the combustion of a liquid fuelcontaining vanadium and sodium. This sample, having a vanadium contentof 0.3%, calculated as vanadium pentoxide, and a sodium contentof0.068%,

calculated as sodium oxide, was heated without an additive for 5 hoursat 900 C. The sand sintered. When the sand sample also contained 0.1%,1.0% or 2.0% by weight of calcium oxide (CaO), its degree of sinteringwas lower in comparison with that of the sample without calcium oxide.

I claim as my invention:

1. In a process for preventing the sinter-ing of a bed of sand particlesdirectly heated by the combustion with air of a liquid hydrocarbon fuelcontaining amounts of a metal of the group consisting of vanadium andsodium sufiicient to cause sintering of said bed, the steps of adding toa bed of sand particles amounts of a material selected from the groupconsisting of magnesium oxide, aluminum oxide, zinc oxide and calciumoxide-to a bed of sand sufiicient to prevent the sintering of said bedand passing hot gases resulting from the combustion of the liquidhydrocarbon fuel with the air through the resulting mixed bed atsnflicient velocity to cause fluidization of said mixed bed.

2. A process as defined in claim 1 wherein the temperature of the mixedbed is maintained at about 900 C.

3. A process as defined in claim 1 in which the material added to thebed of sand particles is magnesium oxide.

4. A process as defined in claim 1 in which the material added to thebed of sand particles is aluminum oxide.

5. A process as defined in claim 1 in which the ma terial added to thebed of sand particles is zinc oxide.

6. A process as defined in claim 1 in which the ma terial added to thebed of sand particles is calcium oxide.

References Cited in the file of this patent UNITED STATES PATENTS2,788,312 Moser Apr. 9, 1957 2,800,172 Romer et al. July 23, 1957FOREIGN PATENTS 445,506 Great Britain Apr. 14, 1936

1. IN A PROCESS FOR PREVENTING THE SINTERING OF A BED OF SAND PARTICLESDIRECTLY HEATED BY THE COMBUSTION WITH AIR OF A LIQUID HYDROCARBON FUELCONTAINING AMOUNTS OF A METAL OF THE GROUP CONSISTING OF VANDIUM ANDSODIUM SUFFICIENT TO CAUSE SINTERING OF SAID BED, THE STEPS OF ADDING TOA BED OF SAND PARTICLES AMOUNTS OF A MATERIAL SELECTED FROM THE GROUPCONSISTING OF MAGNESIUM OXIDE, ALUMINUM OXIDE, ZINC OXIDE AND CALCIUMOXIDE TO A BED OF SAND SUFFICIENT TO PREVENT THE SINTERING OF SAID BEDAND PASSING HOT GASES RESULTING FROM THE COMBUSTION OF THE LIQUIDHYDROCARBON FUEL WITH THE AIR THROUGH THE RESULTING MIXED BED.